Park's Pediatric Cardiology for Practitioners, 6th Ed.

Cardiac Pacemakers and Implantable Cardioverter-Defibrillators in Children

A pacemaker is a device that delivers battery-supplied electrical stimuli over leads to electrodes that are in contact with the heart. It primarily treats bradycardia. An implantable cardioverter-defibrillator (ICD) is a multiprogrammable antiarrhythmic device for treating ventricular tachycardia and ventricular fibrillation. ICDs also possess pacemaking capability to treat bradycardia. The electrical leads are placed either directly over the epicardium or inserted transvenously into the cardiac chambers. Electronic circuitry regulates the timing and characteristics of the stimuli. The power source is usually a lithium–iodine battery.

Physicians encounter an increasing number of children with either temporary or permanent pacemakers. Basic knowledge about the pacemaker and the pacemaker rhythm strip is essential in taking care of these children. This chapter presents examples of electrocardiography (ECG) rhythm strips from children with various types of pacemakers and elementary information regarding pacemaker and ICD therapy in children.

Electrocardiograms of Artificial Cardiac Pacemakers

The need to recognize the rhythm strips of artificial pacemakers has increased in recent years, especially in intensive care and emergency room settings. The position and number of the pacemaker spikes on the ECG rhythm strip are used to recognize different types of pacemakers. Thus, a pacemaker may be classified as a ventricular pacemaker, atrial pacemaker, or P wave–triggered ventricular pacemaker.

1. When the pacemaker stimulates the atrium, the resulting P wave demonstrates an abnormal P axis.

2. When the pacemaker stimulates the ventricle, wide QRS complexes result.

3. The ventricle that is stimulated (or the ventricle on which the pacemaker electrode is placed) can be identified by the morphology of the QRS complexes. With the pacing electrode on the right ventricle, the QRS complex resembles a left bundle branch block (LBBB) pattern; with the pacemaker placed on the left ventricle, a right bundle branch block (RBBB) pattern results.

Ventricular Pacemaker (Ventricular Sensing and Pacing)

This mode of pacing is recognized by vertical pacemaker spikes that initiate ventricular depolarization with wide QRS complexes (Fig. 26-1A). The electronic spike has no fixed relationship with atrial activity (P wave). The pacemaker rate may be fixed (as in Fig. 26-1A), or it may be on a demand (or standby) mode in which the pacemaker fires only after a long pause between the patient’s own ventricular beats.


FIGURE 26-1 Examples of some artificial pacemakers. A, Fixed-rate ventricular pacemaker. Note the regular rate of the electronic spikes with no relationship to the P waves. B, Atrial pacemaker. This tracing is from a 2-year-old child in whom extreme symptomatic bradycardia developed after the Mustard operation. C, P wave–triggered pacemaker. This tracing is from a child in whom surgically induced complete heart block developed after repair of tetralogy of Fallot. Note that in the figure, the electronic spikes are either tall or short but all are of shorter duration. (From Park MK, Guntheroth WG: How to Read Pediatric ECGs, 4th ed., Philadelphia, Mosby, 2006)

Atrial Pacemaker (Atrial Sensing and Pacing)

The atrial pacemaker is recognized by a pacemaker spike followed by an atrial complex; when atrioventricular (AV) conduction is normal, a QRS complex of normal duration follows (see Fig. 26-1B). This type of pacemaker is indicated in patients with sinus node dysfunction with bradycardia. When the patient has high-degree or complete AV block in addition to sinus node dysfunction, an additional ventricular pacemaker may be required (AV sequential pacemaker, not illustrated in Fig. 26-1). The AV sequential pacemaker is recognized by two sets of electronic spikes—one before the P wave, and another before the wide QRS complex.

P Wave–Triggered Ventricular Pacemaker (Atrial Sensing, Ventricular Pacing)

This pacemaker may be recognized by pacemaker spikes that follow the patient’s own P waves at regular PR intervals and with wide QRS complexes (see Fig. 26-1C). The patient’s own P waves are sensed and trigger a ventricular pacemaker after an electronically preset PR interval. This type of pacemaker is the most physiologic and is indicated when the patient has advanced AV block but a normal sinus mechanism. Advantages of this type of pacemaker are that the heart rate varies with physiologic need, and the atrial contraction contributes to ventricular filling and improves cardiac output.

Pacemaker Therapy in Children

Remarkable technologic advances have been made in pacemaker design and function. Surgical corrections of cardiac defects and their late sequelae have increased the need for pacemaker therapy in children. New permanent pacemakers (physiologic pacemakers) are capable of closely mimicking normal cardiac rhythm, and most of them are small enough to be implanted in an infant.


The indications for permanent pacemaker implantation in children are continually evolving as the reliability of pacing systems improves and clinical experience increases. Box 26-1 lists conditions for which pacemaker therapy is or is not indicated based on the 2008 joint recommendations of the American College of Cardiology (ACC), American Heart Association (AHA), and Heart Rhythm Society (HRS) (Epstein et al, 2008). In the guidelines, class I conditions are those for which there is general agreement that the device will be beneficial, and class II conditions are those for which there is ambivalence regarding whether the device will be beneficial. Class IIa conditions are those for which the weight of evidence or opinion is in favor of usefulness or efficacy, and class IIb conditions are those for which usefulness or efficacy is less well established. Class III conditions are those for which there is agreement that the device will not be useful. Each recommendation is accompanied by the weight of evidence as follows. Level A if the data were derived from multiple randomized clinical trials, level B when data were derived either from a limited number of trials or nonrandomized studies, level C when the consensus of experts was the primary source of the recommendation.

BOX 26-1 Recommendations for Permanent Pacing in Children, Adolescents, and Patients with Congenital Heart Disease

Class I (is indicated)

1. For advanced second- or third-degree associated with symptomatic bradycardia, ventricular dysfunction, or low cardiac output (level of evidence: C)

2. For sinus node dysfunction with correlation of symptoms during age-inappropriate bradycardia; the definition of bradycardia varies with the patient’s age and expected heart rate (level of evidence: B)

3. For postoperative advanced second- or third-degree AV block that is not expected to resolve or that persists at least 7 days after cardiac surgery (level of evidence: B)

4. For congenital third-degree AV block with a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction (level of evidence: B)

5. For congenital third-degree AV block in an infant with a ventricular rate less than 55 beats/min or with congenital heart disease and a ventricular rate less than 70 beats/min (level of evidence: C)

Class IIa (is reasonable)

1. For patients with congenital heart disease and sinus bradycardia for the prevention of recurrent episodes of intraatrial reentrant tachycardia; sinus node dysfunction may be intrinsic or secondary to antiarrhythmic treatment (level of evidence: C)

2. For congenital third-degree AV block beyond the first year of life with an average heart rate less than 50 beats/min, abrupt pauses in ventricular rate that are two or three times the basic cycle length, or associated with symptoms caused by chronotropic incompetence (level of evidence: B)

3. For sinus bradycardia with complex congenital heart disease with a resting heart rate less than 40 beats/minor pauses in ventricular rate longer than 3 seconds (level of evidence: C)

4. For patients with congenital heart disease and impaired hemodynamics caused by sinus bradycardia or loss of AV synchrony (level of evidence: C)

5. For unexplained syncope in the patient with prior congenital heart surgery complicated by transient complete heart block with residual fascicular block after a careful evaluation to exclude other causes of syncope (level of evidence: B)

Class IIb (may or might be reasonable)

1. For transient postoperative third-degree AV block that reverts to sinus rhythm with residual bifascicular block (level of evidence: C)

2. For congenital third-degree AV block in asymptomatic children or adolescents with an acceptable rate, a narrow QRS complex, and normal ventricular function (level of evidence: B)

3. For asymptomatic sinus bradycardia after biventricular repair of congenital heart disease with a resting heart rate less than 40 beats/min or pauses in ventricular rate longer than 3 seconds (level of evidence: C)

Class III (is not indicated)

1. For transient postoperative AV block with return of normal AV conduction in an otherwise asymptomatic patient (level of evidence: B)

2. For asymptomatic bifascicular block with or without first-degree AV block after surgery for congenital heart disease in the absence of prior transient complete AV block (level of evidence: C)

3. For asymptomatic type I second-degree AV block (level of evidence: C)

4. For asymptomatic sinus bradycardia with the longest relative risk interval less than 3 seconds and a minimum heart rate more than 40 beats/min (level of evidence: C)

AV, Atrioventricular.

Adapted from Epstein AE, DiMarco JP, Ellenbogan KA, et al. ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices). Circulation 117:2820–2840, 2008.

TABLE 26-1



BPEG, British Pacing and Electrophysiology Group; NASPE, North American Society of Pacing and Electrophysiology.

Adapted from Bernstein AD, Daubert AC, Fletcher RD, et al, and The NASPE/BPEG: The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. Pacing Clin Electrophysiol 25:260-264, 2002.

In general, the most common indications for permanent pacemaker implantation in children, adolescents, and patients with congenital heart disease fit into one of three categories: (1) symptomatic sinus bradycardia (with symptoms of syncope, dizziness, exercise intolerance, or congestive heart failure); (2) the bradycardia–tachycardia syndrome (caused by overdrive suppression after a period of tachycardia); and (3) advanced second- or third-degree AV block, either congenital or postsurgical.

Bradycardia is the most common and noncontroversial indication for permanent pacemaker therapy in both children and adults. The primary criterion for pacemaker implantation for bradycardia is the concurrent observation of a symptom (e.g., syncope) with bradycardia (e.g., heart rate less than 40 beats/min or asystole longer than 3 seconds). In children, significant bradycardia with syncope or near syncope results most commonly from extensive surgery involving the atria (e.g., the Senning operation, the Fontan operation, and surgery for atrial septal defect or total anomalous pulmonary venous return). Another noncontroversial indication is surgically acquired heart block that lasts more than 2 weeks after surgery. The risk of death from surgically acquired heart block is as high as 35% in unpaced patients. Most children with congenital heart block will eventually require pacemaker implantation. Those patients with additional CHDs will require pacemaker therapy at an earlier age than those without heart defects.

Temporary pacing is indicated for (1) patients with advanced second-degree or complete heart block secondary to overdose of certain drugs, myocarditis, or myocardial infarction and (2) certain patients immediately after cardiac surgery.

Types of Pacing Devices

The North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology Group devised a generic letter code to describe the types and functions of pacemakers, and it was updated in 2002 (Table 26-1). The first three letters are used exclusively for antibradyarrhythmia functions.

1. The letter in the first position identifies the chamber paced (O, none; A, atrium; V, ventricle; D, dual chamber; or both A and V).

2. The second is the chamber sensed (O, none; A, atrium; V, ventricle; D, dual).

3. The third letter corresponds to the response of the pacemaker to an intrinsic cardiac event (O, none; I, inhibited; T, triggered; D, dual [I + T]).

4. The fourth letter indicates both programmability and rate modulation.

5. The fifth position of the code is used to indicate whether multisite pacing is present.

Some examples of the first three letters (and their indications) are shown below.

1. A VOO device provides ventricular pacing, no sensing, and no response to an intrinsic cardiac event. This type of pacemaker is commonly used as emergency pacing.

2. An AOO device provides atrial pacing with no sensing.

3. A VVI device is ventricle stimulated and ventricle sensed; it inhibits paced output if endogenous ventricular activity occurs (thus preventing competition with native QRS activity). This type is commonly used for episodic AV block or bradycardia in small infants.

4. An AAI device paces and senses the atrium and is inhibited by the patient’s own atrial activity. This type is commonly used in sinus node dysfunction with intact AV conduction.

5. A DDD device is a dual-chamber pacemaker that is capable of pacing either chamber, sensing activity in either chamber, and either triggering or inhibiting paced output (with resulting AV synchrony). This type is used in AV block where AV synchrony is important.

6. A DVI device paces the ventricle, senses both chambers, and inhibits ventricular pacing. This type allows AV synchrony and is commonly used in patients with atrial arrhythmias.

Selection of Pacing Mode

The pacemaker choice is based on several factors, including the presence or absence of underlying cardiac disease, the size of the patient, and the relevant hemodynamic factors (including the need for atrial contribution in cardiac output).

1. A patient who has sinus node dysfunction but an intact AV node function may receive a single-chamber atrial pacemaker or ventricular pacemaker if AV synchrony is not necessary.

2. In patients with AV block, if AV synchrony is not necessary, a single-chamber ventricular pacing may be implanted.

3. If the sinus node and AV node are both dysfunctional, a dual-chamber device is implanted.

Rate-adaptive pacemakers have the ability to increase the pacing rate through sensors that monitor physiological processes such as activity (activity sensing with vibration detection by piezoelectric crystal or accelerometer) and minute ventilation.

Battery, Leads, and Route

Lithium anode batteries are used almost exclusively. The most widely used type of lithium battery is the lithium iodide. Battery longevity depends on several factors, such as battery size, stimulation frequency, and output per stimulation. Battery life varies from 3 years for a dual-chamber pacemaker used in a small child to 15 years for a large single-chamber device needed infrequently.

There are two types of leads, unipolar and bipolar. The unipolar lead (in which the tip of the lead is the negative pole and the pacemaker itself is the positive pole) has the advantages of a smaller size and a larger sensing circuit, which amplifies low-voltage P waves. The bipolar lead (which possesses a tip electrode [ – ] and a ring electrode [ + ] near the end of the pacing catheter) can screen pectoral muscle “noise,” has a lower likelihood of external muscle stimulation, and can function even if the pacemaker is out of contact with the body.

Historically, epicardial pacing was more common in children, but transvenous implantation is the method of choice. With improved technology, generators and leads have become smaller and more advanced, allowing transvenous pacing systems in small children. In general, the transvenous route is a reasonable approach for children weighing at least 10 kg, although others have reported successful transvenous pacing in neonates without complications. Transvenous implantation is performed on the side contralateral to the dominant hand. Transvenous implantation has several advantages over epicardial implantation: Both atrial and ventricular capture thresholds generally are lower, and pacing problems are significantly fewer than with epicardial implantation. Epicardial implantation is performed through a xyphoid approach and is chosen when a transvenous implantation is precluded, when the patient is a neonate or a small infant (<10 kg), and when the transvenous approach is not possible (after the Fontan operation or superior vena cava obstruction).

Implantable Cardioverter-Defibrillator Therapy

An ICD is used in patients at risk for recurrent, sustained ventricular tachycardia or fibrillation. The efficacy of ICD therapy in saving the lives of patients at high risk of sudden death has been shown convincingly. Multiple studies have shown ICDs to be superior to antiarrhythmic drug therapy in patients with a history of life-threatening ventricular tachyarrhythmias (i.e., ventricular tachycardia or fibrillations).

All ICDs also have a built-in pacemaker. Pacing may be necessary for bradycardia, which may follow an electrical shock delivered by the ICD. The pacemaker also corrects certain tachycardia by overdrive suppression.

The ICD automatically detects, recognizes, and treats tachyarrhythmias and bradyarrhythmias using tiered therapy (i.e., bradycardia pacing, overdrive tachycardia pacing, low-energy cardioversion, high-energy shock defibrillation). They also offer a host of other sophisticated functions (e.g., storage of detected arrhythmic events and the ability to do “noninvasive” electrophysiologic testing). ICDs can discharge voltages ranging from less than 1 V for pacing to 750 V for defibrillation.

The ICD is implanted beneath the skin over the left chest (for right-handed persons) pectoralis muscle and it is then connected to the leads. Virtually all ICD systems are implanted transvenously. The longevity of the ICD depends on the frequency of shock delivery, the degree of pacemaker dependency, and other programmable options, but most are expected to last from 5 to 10 years.

The most common problem with ICDs is inappropriate shocks, which are usually the result of detection of a supraventricular tachycardia, most commonly atrial fibrillation. In adult patients, inappropriate shock has been reported in up to 20% of patients within the first year and 40% by 2 years after implantation, causing pain and anxiety generated by this complication.


Indications for ICD implantation include patients with life-threatening arrhythmias; aborted sudden death; family history of the same disease that can cause sudden death; those with dilated and hypertrophic cardiomyopathy, especially when unexplained fainting episodes have occurred; and other conditions that may increase sudden arrhythmic death risk. The ICD usually is recommended as initial therapy in patients who present with sustained VT or resuscitated cardiac arrest. Box 26-2 lists recommendations for ICD therapy according to the 2008 ACC/AHA/HRS Guidelines (Epstein et al, 2008).

Fewer than 1% of all ICD implantations are performed in pediatric patients.

1. Two most common indications for ICD implantation in children are hypertrophic cardiomyopathy and long QT syndrome.

2. Other potential indications include idiopathic dilated cardiomyopathy, Brugada syndrome, and arrhythmogenic right ventricular (RV) dysplasia.

3. A family history of sudden death may influence the decision to use an ICD in a pediatric patient.

4. Some postoperative CHDs with ventricular tachycardia, such as tetralogy of Fallot and transposition of the great arteries are rare indications for ICD implantation.

Living with a Pacemaker or Implantable Cardioverter-Defibrillator

Electromagnetic interference (EMI) can cause malfunction of the pacemaker or ICD by rate alteration, sensing abnormalities, reprogramming, and other functions, which may result in malfunction of the device or even damage to the pulse generator. EMI is defined as any signal—biological or nonbiological—that is within a frequency spectrum detectable by the sensing circuitry of the pacemaker or ICD.

BOX 26-2 Recommendations for Implantable Cardioverter-Defibrillators in Pediatric Patients and Patients with Congenital Heart Disease

Class I (is indicated)

1. In the survivors of cardiac arrest after evaluation to define the cause of the event and to exclude any reversible causes (level of evidence: B)

2. For patients with symptomatic sustained VT in association with congenital heart disease who have undergone hemodynamic and electrophysiological evaluation; catheter ablation or surgical repair may offer possible alternatives in carefully selected patients (level of evidence: C)

Class IIa (is reasonable)

1. For patients with CHD with recurrent syncope of undetermined origin in the presence of either ventricular dysfunction or inducible ventricular arrhythmias at electrophysiological study (level of evidence: B)

Class IIb (may or might be reasonable)

1. For patients with recurrent syncope associated with complex CHD and advanced systemic ventricular dysfunction when thorough invasive and noninvasive investigations have failed to define a cause (level of evidence: C)

Class III (is not indicated). The same as in adults

1. For patients who do not have a reasonable expectation of survival with an acceptable functional status for at least 1 year even if they meet ICD implantation criteria specific in class I, IIa, and IIb recommendation above (level of evidence: C)

2. For patients with incessant VT or VF (level of evidence: C)

3. In patients with significant psychiatric illness that may be aggravated by device implantation or that may preclude systemic follow-up (level of evidence: C)

4. For NYHA class IV patients with drug-refractory congestive heart failure who are not candidates for cardiac transplantation or CTR-D (level of evidence: C)

5. For syncope of undetermined cause in a patient without inducible ventricular tachycardias and without structural heart disease (level of evidence: C)

6. When VF or VT is amenable to surgical or catheter ablation (e.g., atrial arrhythmias associated with the WPW syndrome, RV or LV outflow tract VT, idiopathic VT, or fascicular VT in the absence of structural heart disease (level of evidence: C)

7. For patients with ventricular tachyarrhythmias caused by a completely reversible disorder in the absence of structural heart disease (e.g., electrolyte imbalance, drugs, or trauma) (level of evidence: B)

CHD, Congenital heart disease; CRT-D, cardiac resynchronization therapy device incorporating both pacing and defibrillation capabilities. LV, left ventricular; NYHA, New York Heart Association; RV, right ventricular; VF, ventricular fibrillation; VT, ventricular tachycardia; WPW, Wolff-Parkinson-White.

Adapted from Epstein AE, DiMarco JP, Ellenbogan KA, et al. ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices). Circulation 117:2820–2840, 2008.

Patients should be well educated to avoid situations that may cause malfunction or damage to the device. EMI can occur within or outside the hospital. The patient with pacemakers or ICDs should wear a medical identification bracelet or necklace to show that he or she has a pacemaker or ICD in case of emergency. The following lists some common situations which may or may not affect pacemakers or ICDs.

1. Most home appliances will not interfere with the pacemaker signal. The following home appliances are safe to use.

a. Kitchen appliances (microwave ovens, blenders, toaster ovens, electric knives)

b. Televisions, stereos, FM and AM radios, ham radios, and CB radios

c. Electric blankets, heating pads,

d. Electric shavers, hair dryers, curling irons

e. Garage door openers, gardening electric trimmers

f. Computers, copying and fax machines

g. Properly grounded shop tools (except power generator or arc welding equipment)

2. The patient must use caution in the following situations.

a. Security detectors at airport and government buildings such as courthouse. The patient should not stay near the electronic article surveillance (EAS) system longer than is necessary and should not lean against the system.

b. Cellular phones: one should not carry a cell phone in the breast pocket when the ICD is implanted in the left upper chest. Keep the cell phone at least 6 inches away from the ICD. When talking on the cell phone, hold it on the opposite side of the body from the ICD.

c. Avoid working with, holding, or carrying magnets near the pacemaker.

d. Turn off large motors such as cars or boats when working on them. Do not use a chainsaw.

e. Avoid industrial welding equipment. Most welding equipment used for hobby welding should not cause any significant problem.

f. Avoid high-tension wires, radar installations, smelting furnaces, electric steel furnaces, and other high-current industrial equipment.

g. Abstain from diathermy (the use of heat to treat muscles).

h. Contact sports are not recommended for children with pacemakers or ICDs.

3. Hospital sources of potentially significant EMI are as follows.

a. Electrocautery during surgical procedures: Notify the surgeon or dentist so that electrocautery will not be used to control bleeding. ICD therapy should be deactivated before surgery and reinitiated after surgery by a qualified professional. Alternatively, a magnet can be placed over the pacemaker throughout the procedure.

b. For cardioversion or defibrillation: Paddles should be placed in the anteroposterior position, keeping the paddles at least 4 inches from the pulse generator. A qualified pacemaker programmer should be available.

c. Magnetic resonance imaging is considered a relative contraindication in patients with a pacemaker or ICD.

Follow-up for Pacemaker and Implantable Cardioverter-Defibrillator

Patients with pacemakers and ICDs must be followed on a regular schedule. Many of the same considerations are relevant to both pacemaker and ICD follow-up. The follow-up schedule varies from institution to institution, but one popular approach is to see the child 2 weeks after cardiac pacemaker implantation to make sure that the incisions are healing well and there is no electrode dislodgement. A repeat follow-up appointment is scheduled at 6 weeks. Subsequent visits are scheduled at 3 months, 6 months, and 1 year. Thereafter, visits are usually done once every 12 months for single-chamber pacemakers and once every 6 months for dual-chamber pacemakers.

After the initial pacemaker follow-ups, some physicians prefer regular office assessment, others prefer transtelephonic follow-up, and still others prefer a combination of the two techniques. Monthly transtelephonic pacing system evaluation is simple, convenient, and relatively inexpensive, allowing follow-up with fewer cardiology office visits. Transtelephonic assessment includes a collection of (1) a nonmagnet ECG strip, (2) an ECG strip with magnet applied to the pacemaker, and (3) measurement of magnet rate (see below for a discussion of an ECG with magnet application) and pulse duration. (Pulse duration is measured on both atrial and ventricular channels for dual-chamber pacemaker.) During an office visit, the clinical status of the patient is assessed, and the same information as described for transtelephonic assessment should be collected.

ECG and magnet application. The 12-lead ECG with and without a magnet (placed over a pacemaker generator) is a useful tool in pacemaker follow-up assessment.

1. The integrity of atrial and ventricular pacing can be quickly identified with magnet placement. Without the magnet, the patient’s intrinsic rhythm inhibits pacer firing.

2. With the magnet on, it begins to pace at a fixed rate in an asynchronous mode (or “magnet mode”). It does not sense the patient’s own rhythm (i.e., it paces at a fixed rate regardless of what the patient’s own heart rhythm is).

3. The fixed rate that a pacemaker paces at after magnet placement is termed the magnet rate. A decrease in the magnet rate (e.g., from the fixed pacing rate of 85 beats/min to 75 beats/min) over time is indicative of a pacemaker battery that is beginning to wear down.

4. It will help locate the side of the ventricle paced (i.e., RBBB pattern with left ventricular pacing and LBBB pattern with RB pacing. Whereas a superior QRS axis suggests leads in the RV apex, an intermediate or inferiorly directed QRS axis suggests leads high on the septum or in the outflow tract.

In many institutions, ICD follow-up is similar to pacemaker follow-up. For an ICD follow-up, the following specific information is collected and assessed. Many cardiologists follow up every 3 to 6 months for the first 3 to 4 years, after which follow-up frequency increases.

1. History: specific emphasis on awareness of delivered therapy and any tachycardia events

2. Device interrogation

3. Assessment of battery status and charge time

4. Retrieval and assessment of stored diagnostic data, such as the cycle length or rate of the detected tachyarrhythmias and ECGs of detected arrhythmias

5. Periodic radiographic assessment

6. Periodic arrhythmia induction in the electrophysiology laboratory to assess defibrillation threshold and efficacy